International Journal of ChemTech Research
CODEN (USA): IJCRGG
ISSN : 0974-4290
Vol.6, No.5, pp 2783-2787, Aug-Sept 2014
Factors Affecting Printing Quality of Paper from Bagasse Pulp
K. Kumaraguru, M. Rengasamy*, E. Titus Praveen Kumar, D. Venkadesh
Department of petrochemical technology, Anna University (BIT Campus),
Tiruchirappalli- 620024, TN, India.
*Corres.author: [email protected]
Abstract: The printing industry is the largest collective consumer of paper products and estimated that around
43 trillion papers are used for printing annually across the country. As the printing industry continues to reduce
the cost and improve the quality of paper, the effective measurement of printing quality is very important. Most
common problems affecting a bagasse pulp printing paper includes pulping, piling, linting, warm weather
complaints, cold weather complaints, effect of press moisture, grain long, pH problems and types of picking.
This paper reviews about various problems occurring in printing a paper produced from bagasse pulp, causes
for problem during printing and their corrective actions to be taken to improve the printing quality.
Keywords: printing factors, bagasse pulp, printing quality.
1. Introduction
Printing is a process by which qualities of images are produced on paper or another substrate, using a
printing plate or image carrier, ink, with a help of printing press. The impact of printing has a day to day effect
around the world. The members of this industry call printing as “the art preservative of all the arts” (1). This is
due to the fact that with the aid of this invention we are able to make permanent records of current events.
The quality of a printing paper is an important factor to decide the quality of printing over it (2).
Globally, the main challenges of the printing industries are to meet the global market need in such a way to
produce paper of different specifications, depends upon its usage (3). Some papers are suitable for any one
specific purpose, like security papers are used for money printing, for representing values, etc. while others may
be suitable for two or more printing purpose like computer printing, toilet paper, newspapers, etc (3, 4).
2. Printing Process
Various printing process techniques are used for printing purpose. Three basic methods are commonly
used for direct or contact printing (4)
* Relief method (From a raised surface)
Relief letter press and flexography
* Planographic method (From a flat surface)
Lithography (offset) screen-printing and mono-prints.
* Intaglio method (From a recessed area)
Engraving, dry-point, etching, aquatint and mezzotint.
Printing Process Requirements
The papermaker needs to understand the requirements of the printer in order to produce suitable papers
for printing. Runnability and printability are the two major factors need to be considered while printing
(4, 5).
M. Rengasamy et al /Int.J. ChemTech Res.2014,6(5),pp 2783-2787.
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Runnability
Runnability is the process in which the paper passes through the press without breaks. It leads to
produce trouble free printing process and high productivity (5). A poor running sheet will cause
problems or necessitate slow operation of the presses which adversely affects the economics of printing.
It is also important from a runnablity standpoint that the paper rolls or a pallet of paper starts to arrive at
the press room in good mechanical condition. Paper strength, uniformity and freedom from defects are
the important properties which affects the runnability during printing.
•
Printability
Printability is the effect of the reproduction of the images sharply and correctly without the
displacement of ink on the paper. Printability is the interacting result of different paper-related factors
in printing process, which contribute to the full use of the quality potential of the paper in the print
process (4).
Parameters for printability are mainly their properties that influence the visual quality of a printed
product. Printability is not the same as print quality because print quality is also determined by other
factors of printing technology (5).
Brightness, opacity, gloss, smoothness, porosity, and sizing are the important properties of paper, but
the requirements may vary based on the printing process. Typically, coated papers have better
appearance than uncoated paper (6), due to impressed smoothness, brightness and gloss.
Pulping
Pulping is a process which extracts fibrous material and cellulose from wood or other raw materials as a
prelude during paper making (3). The purpose of pulping is to liberate cellular fibres from other
chemicals and other impurities in the wood. Before wood can be pulped, it should undergo debarking.
Bark contains little or no fibrous material. It can be removed either mechanically or hydraulically.
Usually debarked woods are used for pulping.
•
Bagasse Pulp
Bagasse is an agricultural residue in which mainly fibrous material remains. Paper making with
bagasse, as the major raw material (4, 5) has been posing several challenges as
•
Bagasse is a bulky raw material and is difficult to handle.
•
Bagasse requires mild bleaching and refining conditions to avoid damage to the fibre.
3. Factors Affecting Printing Quality
Pulping and paper making are the preliminary aspects of the paper quality product. The real challenge
comes when the product is put into its intended fundamental end printing industry (7). The following are the
various factors that affect the printability of paper. The reasons and their solutions are discussed.
•
Bagasse Pulp Properties vs Printability
Role of Oil Absorbency and Paper Porosity
Various printing processes require inks for printing different characteristics. An ink’s dyeing
time depends on the physical attributes of a paper. Mainly the printability property is influenced notably
by oil absorbing nature of the base pulp. Pulp having more oil absorbency tends to take more ink (9).
Too high oil absorbency is reported to cause more show since excess oil reduces the opacity of the
paper and tends to make it transparent after printing.
M. Rengasamy et al /Int.J. ChemTech Res.2014,6(5),pp 2783-2787.
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Improving Porosity and Oil Absorbency
The presence of pith (parenchyma cells) in bagasse results to form a close sheet with low
porosity and oil absorbency (9). The oil absorbency is directly proportional to the porosity of the sheet.
Low oil absorbency of bagasse based paper tends to take-up low ink, i.e. the ink demand for bagasse
paper is low. Fast drying ink and heat set offset process are best suited for low porosity paper. Further
studies need to be on ink formulation for agricultural residue base paper, since the ink used for normal
wood based paper needs modification for bagasse based paper.
Improving porosity of a paper in case of bagasse is very difficult due its closeness of sheet
formed due to presence of amorphous pith. Use of fillers of high surface area, will fill the inter fibre
space and improves the porosity of paper (9). Earlier studies reveal that among the various fillers,
precipitated calcium carbonate gives a profound increase in porosity particularly bagasse paper,
whereas wet consolidation of the sheet does not improve the porosity.
•
Grain
Grain-short paper is specified for making black and white or single colour work with good folding
(or) economical layout. But even here, a wavy-edged (or) tight edged condition can develop along with the
gripper edge which causes trouble in feeding on any type of press (or) offset duplicator.
Bad register in multi-colour printing by using short grain paper may stretch greater (or) shrink
greater (7). These problems occur in a printing paper due to low stiffness in short grain. In order to avoid
stretching or shrinking of image printing long grain paper can be recommended.
•
Fountain Solution
A mixture of water and other chemicals distributed by the dampening system on a printing press is used
in offset lithography. A fountain solution may contain a drying stimulator which works to enhance the
effectiveness of the dryer when mixed with the ink(8).
In this technique, emulsification problem, scrumming and drying difficulties are the major
problems in a printing paper. These problems are due to pH variations of the fountain solution, higher or
lower the value of pH may affect the quality of printing to a greater extent. These problems can be
prevented by maintaining the pH range constant in the range 4.7-6.0 with the help of chemical buffer
system with good buffer capacity.
•
Bulk Problem
One of the most important characteristics that affect the printing is bulk or specific volume. It is the
inherent nature of the raw material used in the printing (9). Two approaches are possible to improve the
bulk, since low bulk has to improve for getting the improved resiliency during printing by addition of fillers
like PCC (precipitated calcium carbonate) or inclusion of some amount of high bulk pulps such as hard
woods and soft woods (10).
•
Dimensional Problem
One of the major problems in offset printing is the curls and changes in paper dimension design.
These are mainly caused by absorption of water, softening and weakening of the paper surface, which leads
to picking and transfer of excessive moisture from the press dampening system (11). Proper sizing of the
paper can avoid the above said problem.
•
Piling
Piling is a printing problem caused by the accumulation of paper fibres, bits of detached coating
particles and other debris on the printing plates or blankets in the image or non-image areas. Piling can be
occurred by various reasons in addition to basic surface debris.
This is caused mainly due to the improper formation and sizing of the bagasse paper during
production. This can be avoided by improving bonding, by increasing the efficient sizing and using the
tackier inks that overcome the paper’s pick resistance.
M. Rengasamy et al /Int.J. ChemTech Res.2014,6(5),pp 2783-2787.
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Strike-Through
Strike through is an often encountered print quality problem caused by ink penetration and insufficient
opacity of paper. If the strike-through of a paper is high, it leads to very dull images and an impact on the
other side of the paper.
The rate of absorption has a direct impact on the strike-through of a paper. The strike through of a paper
is very large when the rate of absorption is high. This can be avoided by using suitable filler during paper
making.
•
Linting
Linting is described as the tendency of a paper to shed loosely bound fibres and fines that decrease the
quality of a paper. White fibre shaped spots, short life of the printing plates are the reasons for linting (8).
Bonding of fibre to the surface of paper is not complete. Tacky ink picks up the loose fibre as they
accumulate on the blankets and rollers of the press. The fibres absorb water and when they are saturated,
they repel ink. This can be avoided by improving the quality of paper surfaces.
•
Moisture Content
Moisture content directly affects reliability and print quality. Too much moisture can cause excessive
curls, jams and print quality problems. Too low moisture level can cause static problems, which can also
lead to jams as well as cause difficulties in post-processing paper handling (10). This can be avoided by
using the paper which has the moisture content of 4.5%. Moisture proof reaming papers are essential to
maintain the correct moisture level of paper.
•
Hot & Cold Weather Complaints
Wavy edges, wrinkled sheets, tight edges, shrinking and retarded ink drying are the most common
complaints during printing and paper manufacture during heavy rain and humidity create wavy edges and
cockling papers to wrinkle. It leads to increase in calliper and basis weight. Winter coldness and dryness
cause static to plague printers. This can be avoided by storing and printing in a well-controlled temperature
and humidity conditions (8).
•
Smoothness
The smoothness of paper has a significant impact on quality of the image. The image quality degrades
when the paper is too rough. An extremely rough paper does not allow proper toner diffusing. Digital color
grade and coated paper are used for better quality printing requirement (7).
•
Picking
Papers can exhibit picking when subjected to high stress, which develops during ink application. There
are two types of picking namely dry and wet picking. Dry picking occurs when oil based ink is used in
printing. When an offset process uses water additionally, that may weaken the coating further leads to form
Wet picking (11).
This can be avoided by using binder in sufficient amounts based on the binder demands.
•
Gloss Level
The gloss level of paper is measured by the ratio of reflected to incident light. It is the reflectance of the
surface, responsible for its shiny or lustrous appearance (6). A higher gloss is achieved by making the
surface more reflective through a combination of calendaring (pressing) and/or coating choices.
4. Conclusion
Nowadays the recent advancement in paper making technology is a boon to the industry. By
maintaining the above pre and post paper making process, we can get good quality of printing. Though risk and
cost remain main criteria in decision making process, when these factors are balanced in a long term vision
M. Rengasamy et al /Int.J. ChemTech Res.2014,6(5),pp 2783-2787.
2787
through ambience, it can produce paper from bagasse pulp and create innovating opportunities in challenging
the global market demand rarely.
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Cobb, R.M.K, “Coating adhesive demand – what pigment function governs it ?”, TAPPI J., 1958, 41
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*****
M. Rengasamy et al /Int.J. ChemTech Res.2014,6(5),pp 2783-2787.
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